Various prior art devices have been developed that are configured to capture an image from within in vivo passages and cavities within an organism's body, such as cavities, ducts, and tubular organs within the gastrointestinal (GI) tract. Several prior art devices are formed as a capsule dimensioned small enough to be swallowed. The capsule typically holds a camera and one or more light sources for illuminating an object outside the capsule whose image is recorded by the camera. The electronics in the capsule may be powered by batteries or by inductive power transfer from outside the body. The capsule may also contain memory for storing captured images and/or a radio transmitter for transmitting data to an ex vivo receiver outside the body. A common diagnostic procedure involves a living organism (such as a human or animal) swallowing the capsule, followed by the camera in the capsule capturing images at various intervals as the capsule moves passively through the organism's cavities formed by inside tissue walls of the GI tract under the action of peristalsis.
Two general image-capture scenarios may be envisioned, depending on the size of the organ imaged. In relatively constricted passages, such as the esophagus and the small intestine, a capsule which is oblong and of length less than the diameter of the passage, will naturally align itself longitudinally within the passage. In several prior art capsules, the camera is situated under a transparent dome at one (or both) ends of the capsule. The camera faces down the passage so that the center of the image is formed by a dark hole. The field of interest is the intestinal wall at the periphery of the image.
FIG. 1A illustrates an in vivo camera capsule 100 of the prior art. Capsule 100 includes a housing that can travel in vivo inside an organ 102, such as an esophagus or a small intestine, within an interior cavity 104 of the organ. In the image-capture scenario shown in FIG. 1A, capsule 100 is in contact with an inner surface 106 of the organ, and the camera lens opening 110 captures images within its field of view 128. The capsule 100 may include an output port 114 for outputting image data, a power supply 116 for powering components of the camera, a memory 118 for storing images, compression circuitry 120 for compressing images to be stored in memory, an image processor 122 for processing image data, and LEDs 126 for illuminating surface 106 of the organ so that images can be captured from the light that is scattered off of the surface.
A second scenario occurs when a capsule is in a cavity, such as the colon, whose diameter is larger than any dimension of the capsule. In this scenario the capsule orientation is much less predictable, unless some mechanism stabilizes it. Assuming that the organ is empty of food, feces, and fluids, the primary forces acting on the capsule are gravity, surface tension, friction, and the force of the cavity wall pressing against the capsule. The cavity applies pressure to the capsule, both as a passive reaction to other forces such as gravity pushing the capsule against it and as the periodic active pressure of peristalsis. These forces determine the dynamics of the capsule's movement and its orientation during periods of stasis. The magnitude and direction of each of these forces is influenced by the physical characteristics of the capsule and the cavity. For example, the greater the mass of the capsule, the greater the force of gravity will be, and the smoother the capsule, the less the force of friction. Undulations in the wall of the colon tend to tip the capsule such that a longitudinal axis 118 of the capsule is not parallel to the longitudinal axis of the colon.
FIG. 1B shows an example of a passage 134, such as a human colon, with capsule 100 in contact with surface 132 on the left side of the figure. In this case, an optical axis (not shown) of the camera is parallel to the longitudinal axis of passage 134 (both axes are oriented vertically in the figure). Capsule 100 also has a longitudinal axis 118 that is coincident with its camera's optical axis. A ridge 136 in passage 134 has a front surface 138 which is visible and thus imaged by capsule 100 as it approaches the ridge (assuming capsule 100 moves upwards in the figure). Backside 140 of ridge 136, however, is not visible to the lens opening 110, and hence does not form an image of backside 140. Specifically, capsule 100 misses part of surface 140 and note that it misses an irregularity in passage 134, illustrated as polyp 142.
In FIG. 1B, three points within the field of view of lens opening 110 are labeled A, B and C. The distance of lens opening 110 is different for these three points, where the range of the view 112 is broader on one side of the capsule than the other, so that a large depth of field is required to produce adequate focus for all three simultaneously. Also, if the LED (light emitting diode) illuminators provide uniform flux across the angular FOV, then point A will be more brightly illuminated than points B and C. Thus, an optimal exposure for point B results in over exposure at point A and under exposure at point C. An optimal exposure for point A results in under exposure at points B and C. For each image, only a relatively small percentage of the FOV will have proper focus and exposure, making the system inefficient. Power is expended on every portion of the image by the flash and by the imager, which might be an array of CMOS or CCD pixels. Moreover, without image compression, further system resources are expended to store or transmit portions of images with low information content. In order to maximize the likelihood that all surfaces within the colon are adequately imaged, a significant redundancy, that is, multiple overlapping images, is required in using this prior art capsule.
U.S. Pat. No. 6,836,377 and U.S. Pat. No. 6,918,872 disclose two prior art geometries for non-panoramic capsule cameras. In U.S. Pat. No. 6,836,377, the capsule dome is ellipsoidal with the pupil at its center and LEDs lying on the focal curve. In U.S. Pat. No. 6,918,872, the dome is spherical with the pupil centered on the center of curvature and LEDs in the same plane further toward the edge of the sphere. The just-described two patents are incorporated by reference herein in their entirety, as background. Various illumination geometries for capsule endoscopes with panoramic imaging systems are disclosed in U.S. patent application Ser. No. 11/642,285 filed on Dec. 19, 2006 by Kang-Huai Wang and Gordon Wilson entitled “In Vivo Sensor with Panoramic Camera” and assigned to CapsoVision, Inc. The just-described patent application is incorporated by reference herein in its entirety.
US Patent Publication 2006/0178557 by Mintchev et al. entitled “Self-Stabilizing Encapsulated Imaging System” is incorporated by reference herein in its entirety as background. This publication describes a capsule endoscope illustrated in FIG. 1C attached hereto, wherein a light emitting diode (LED) 154 and an imager 152 (e.g. a CMOS imager) are mounted in a central region of a capsule, between ends 156a and 156b. The capsule includes an RF transmitter 158 that transmits images acquired by imager 152 to an external receiver. The capsule also includes batteries 160a and 160b, and a controller 162.
The inventor believes that improvements in illumination for imaging in vivo passages by endoscopes are desired.